Backside Ohmic Contact Structure With Metallic Implant
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Solution Overview
Problem
Current methods for forming backside ohmic contacts in semiconductor devices face challenges such as poor adhesion of sputtered metal layers due to oxidation, high contact resistance, and limited manufacturing process flexibility.
Innovation Solution
The approach involves performing a blanket metallic implant on the backside of a semiconductor substrate, followed by the formation of a metallic layer, which together define a low-resistance ohmic contact. This method includes grinding, silicon etching, impurity implantation, and laser annealing to prepare the substrate, and using metallic implants like aluminum with optional additional metals to form a silicon-metal alloy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sputtering process is used to deposit metallic layers on backside, then metal layers can be formed, but adhesion is poor due to oxidation during preparation time
Solution Approach 1:
The patent performs preliminary actions by depositing the first metallic material layer and forming the ohmic contact structure before the semiconductor wafer is exposed to oxidizing environments during subsequent processing steps. This preliminary formation of the contact structure ensures that the critical interface between the metallic material and semiconductor substrate is established before oxidation can occur, thereby maintaining good adhesion without requiring extremely tight process timing.
Solution Approach 2:
The patent employs inert atmosphere processing by conducting the sputtering deposition and contact formation steps in a controlled inert or reducing atmosphere environment. This prevents oxidation of the semiconductor substrate surface and the metallic material layers during the preparation and deposition process, thereby ensuring good adhesion between the metallic layers and the substrate without limiting the process time window.
2Ease of manufacture
If wet chemistry etch process is used to prepare backside surface, then surface preparation is achieved, but process complexity increases
Solution Approach 1:
The patent extracts and eliminates the wet chemistry etch process step from the traditional backside contact formation sequence. Instead of using wet etching to prepare the backside surface, the patent directly proceeds to deposit the metallic material layers via sputtering onto the as-received or minimally prepared backside surface. This removal of the wet etch step simplifies the overall process while still achieving the necessary surface preparation through the sputtering process itself, which can provide both cleaning and deposition functions in one step.
3Reliability
If sputtering is used for metal deposition, then layers can be formed, but contact resistance is high due to target variability
Solution Approach 1:
The patent employs composite material structures by forming a multi-layer metallic contact structure consisting of a first metallic material layer (such as tungsten or molybdenum) and a second metallic material layer (such as aluminum or copper). This composite structure compensates for the limitations of individual materials and sputtering process variability. The first layer provides good adhesion and low contact resistance to the semiconductor substrate, while the second layer provides low resistance and good conductivity, together achieving stable and reliable ohmic contacts despite sputtering target variability.
Solution Approach 2:
The patent utilizes parameter changes by carefully controlling and optimizing the sputtering deposition parameters including power density, gas pressure, deposition temperature, and layer thicknesses. By adjusting these parameters, the patent achieves consistent material properties and interface characteristics that reduce contact resistance and improve process stability, overcoming the inherent variability of sputtering target performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method reduces backside contact resistance, enhances manufacturing process flexibility by eliminating the need for wet chemistry etching and initial sputtering, and improves the performance of semiconductor devices by reducing collector-to-emitter saturation voltage and drain-to-source on resistance.
Implementation Method 1
a metallic implant disposed in the substrate, the metallic implant being a blanket implant on the second side of the substrate
Implementation Method 2
performing a laser anneal on the second side of the semiconductor substrate
Data Source
AI summary
In some aspects, the techniques described herein relate to a semiconductor device including: a substrate having a first side and a second side, the second side being opposite the first side; active circuitry disposed on the first side of the substrate; a metallic implant disposed in the substrate, the metallic implant being a blanket implant on the second side of the substrate; and a metallic layer disposed on the second side of the substrate, the metallic layer and the second side of the substrate including the metallic implant defining an ohmic contact.